There has long been a need for a thread cutting aid which will permit near perfect alignment of the thread cutter with the pipe work piece; will permit starting and finishing of the thread cutting using one hand and permit the thread repair and cutting in close quarters ordinarily not reachable using prior art tools.
Various attempts have been made in the prior art to solve the above indicated problems. However, as will be apparent from the discussion of the two patents below, these attempts have proved unsuccessful.
U.S. Pat. No. 2,273,598 issued Feb. 17, 1942 to C. W. Shafer, is directed to a die stock. The die stock of the Shafer Patent employs a fixed or buttonhead die such as is used for the threading of bolts. The Shafer die stock provides a guiding head carrying the button die in such manner that chips, formed by placing threads onto bolts, will readily clear from the bolt being threaded. Shafer accomplishes this by mounting the button die in one end of a tubular head, the other end portion of which constitutes the pipe guide, and is acted on externally by means to rotate the head, while between the driving portion and the die-carrying portion, the head has lateral openings which lead directly to the region at the inner face of the die.
The patentee states that the die-carrying head, is a very simple device which preferably contains one single integral steel casting which receives a cutting die of standard configuration and effectively holds it in position thus enabling its ready rotation while the guiding sleeve coacts with the bolt being threaded maintaining the die exactly perpendicular to the bolt axis. This structure is stated to be associated with clearance passageways which discharge the chips as they are formed and is said to prevent any clogging at the teeth.
U.S. Pat. No. 4,927,302 issued to Robert A. Beaty on May 22, 1990, is directed to a threading device which can cut a uniform and symmetrical screw thread in the outer surface of a round bar or tube. The Beaty threading device includes a die nut having internal cutting threads and two axial holes and a guide ring which includes two axial roll pins extending away from a rear face thereof and which are capable of extending into the axial holes in the die nut without play to align the axis of the guide ring with the axis of the die nut. The guide ring is stated to act to maintain the axis of the die nut coaxial with the axis of a round bar or tube which extends through the bore of the guide ring and contacts the cutting threads in the die nut. The die nut, together with the guide ring, can be manually rotated to cut a screw thread in a round bar or tube by means of a conventional wrench.